Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
  • B01F25/00—Flow mixers; Mixers for falling materials, e.g. solid particles
  • B01F25/40—Static mixers
  • B01F25/44—Mixers in which the components are pressed through slits
  • B01F25/441—Mixers in which the components are pressed through slits characterised by the configuration of the surfaces forming the slits
  • B01F25/4412—Mixers in which the components are pressed through slits characterised by the configuration of the surfaces forming the slits the slits being formed between opposed planar surfaces, e.g. pushed again each other by springs
  • B01F25/44121—Mixers in which the components are pressed through slits characterised by the configuration of the surfaces forming the slits the slits being formed between opposed planar surfaces, e.g. pushed again each other by springs with a plurality of parallel slits, e.g. formed between stacked plates
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
  • B01F25/00—Flow mixers; Mixers for falling materials, e.g. solid particles
  • B01F25/40—Static mixers
  • B01F25/44—Mixers in which the components are pressed through slits
  • B01F25/442—Mixers in which the components are pressed through slits characterised by the relative position of the surfaces during operation
  • B01F25/4421—Mixers in which the components are pressed through slits characterised by the relative position of the surfaces during operation the surfaces being maintained in a fixed position, spaced from each other, therefore maintaining the slit always open

Definitions

• Homogenization is the process of breaking down and blending components within a fluid.
• One familiar example is milk homogenization in which milk fat globules are broken-up and distributed into the bulk of the milk.
• Homogenization is also used to process other emulsions such as silicone oil and process dispersions such as pigments, antacids, and some paper coatings.
• the most common device for performing homogenization is a homogenization valve.
• the emulsion or dispersion is introduced under high pressure into the valve, which functions as a flow restrictor to generate intense turbulence.
• the high pressure fluid is forced out through a usually narrow valve gap into a lower pressure environment .
• Newer homogenization valve designs have been more successful at accommodating high flow rates while maintaining optimal valve gaps. Some of the best examples of these designs are disclosed in United States Patent Nos . 4,352,573 and 4,383,769 to William D. Pandolfe and assigned to the instant assignee, the teachings of these patents being incorporated herein in their entirety by this reference.
• Multiple, annular, valve members are stacked one on top of the other.
• the central holes of the stacked members define a common, typically high pressure, chamber.
• Annular grooves are formed on the top and/or bottom surfaces of each valve member, concentric with the central hole.
• the grooves are in fluid communication with each other via axially directed circular ports that extend through the members, and together the grooves and ports define a second, typically low pressure, chamber.
• each valve member the wall between the central hole and the grooves is chamfered to provide knife edges.
• Each knife edge forms a valve seat spaced a small distance from an opposed valve surface on the adjacent valve member. In this design, an optimal valve spacing can be maintained for any flow rate; higher flow rates are accommodated simply by adding more valve members to the stack.
• homogenization valve design is generally driven by two concerns.
• milk shelf life is limited by the time between homogenization and when creaming begins to affect visual appearance. This is the reverse of the homogenization process in which the milk fat again becomes separated from the bulk milk.
• the second, sometimes conflicting, concern is the cost of homogenization, which is largely dictated by the consumed energy.
• the size of the milk fat globules in the homogenized milk determines the speed at which creaming occurs. Thus, in order to extend shelf life, it is important that the homogenization process yields small fat globules in the homogenized milk. The smaller the fat globules, the more dispersed is the fat, and the longer it takes for enough of the fat globules to coalesce and produce noticeable creaming. More complete homogenization, however, generally requires higher pressures, which undermines the second concern since higher pressures require larger energy inputs . The standard deviation in the size of the fat globules in the homogenized milk, however, also plays a role in determining the milk's shelf life.
• Some valve designs produce generally small fat globules, which suggests a long shelf life. Because of the characteristics of the regions surrounding the valve gap, however, some fat globules can largely or entirely escape the homogenization process as they pass through the valve. These larger fat globules in the homogenized milk contain a relatively large amount of fat, and they cream rapidly compared to very small fat globules. Thus, even though the average size of the fat globules may be small in a given sample of milk, the shelf life may still be relatively short due to the existence of a relatively few large globules.
• the present invention is directed to an improved valve member design that is applicable to the design disclosed in the Pandolfe series of patents. More generally, the principals of the present invention may be applied to other homogenization valve configurations.
• the invention concerns a homogenizer valve in which flow restricting surfaces oppose each other on either side of a laterally extended valve gap.
• the downstream terminations of the opposed surfaces are staggered with respect to each other by at least a distance necessary to inhibit chattering of the valve.
• downstream terminations of the opposed surfaces in the preferred embodiment should be staggered by at least a height of the valve gap for stability, but staggered not more than approximately ten of the gap heights for complete homogenization.
• the preferred homogenizer valve comprises a stack of annularly-shaped valve members defining a central hole and axial fluid conduits. This configuration is applicable in commercial applications requiring flow rates of 500 gal/min and greater. Annular springs are used to align adjoining pairs of the valve members, the springs fitting in spring- grooves formed in the valve members. Homogenization occurs as the fluid passes between the central hole and the axial fluid conduits through the intervening annular valve gaps.
• one of the opposed surfaces in each adjoining pair of the valve members is a knife edge land, which has a total length of preferably between 0.015 to 0.020 inches, but always less than 0.06 inches.
• Fig. 1 is a cross sectional view of a homogenization system showing valve members according to the present invention
• Fig. 2 is a perspective and partially cut-away view of the inventive valve members in a valve member stack in the homogenization system
• Fig. 3 is a partial vertical cross-sectional view of the stacked valve members showing the valve gap region for a prior art homogenization valve and the inventive homogenization valve;
• Fig. 4 is a cross-sectional view of the prior art valve gap region and the flow conditions for the fluid emerging through the valve gap;
• Fig. 5 is a cross-sectional view of the valve gap region in which no overlap exists between the upper and lower surfaces of the nozzle aperture according to the present invention
• Fig. 6 is a cross-sectional view of the valve region showing a valve with only moderate overlap according to the present invention
• Fig. 7 is a plot of the droplet size as a function of homogenizing pressure for various valve overlap distances during commercial-scale milk homogenization.
• Fig. 8 is a plot of droplet diameter as a function of overlap for various homogenizing pressures using filled milk at a flow rate of 40 gallons per hour.
• Fig. 1 is a cross-sectional view of a homogenization system that is related to the design disclosed in the Pandolfe patents.
• the system includes valve members 100 constructed according to the principles of the present invention, many of the details of these members being better understood with reference to Fig. 2.
• an inlet port 112 formed in an inlet flange 114 conveys a high pressure fluid to a valve member stack 116.
• the high pressure fluid is introduced into an inner chamber 118 defined by the central holes 103 formed through the generally annular valve members 100.
• the high pressure fluid is then expressed through valve gaps 102 into a low pressure chamber 120 that is defined by the axial ports 122 through the valve members 100 and the annular grooves 124 in the valve members.
• the fluid passing into the low pressure chamber enters a discharge port 126 in a discharge flange assembly 130.
• the stack 116 of valve members 100 is sealed against the inlet flange 114 via a base valve member 132.
• the top- most valve member engages a top valve plug 140 that seals across the inner chamber 118.
• This top valve plug 140 is hydraulically or pneumatically urged by actuator assembly 142 , which comprises an actuator body 144 surrounding an actuator piston 146 sealed to it via an O ring 148.
• the piston 146 is connected to the top plug 140 via the actuator rod 150.
• An actuator guide plate 152 sits between the body 144 and the discharge flange assembly 130.
• Fig. 3 is a cross-sectional view of the valve members around the valve gaps, showing a prior art valve gap region 160 and the valve gap region 170 in the inventive homogenization valve.
• the height of both gaps is preferably between 0.0015 and 0.0020 inches, usually about 0.0018 inches, but in any event less than 0.003 inches. This dimension is defined as the vertical distance between the valve seat or land 158 and the opposed, largely flat, valve surface 156. Experimention has shown that the gap should not be simply increased beyond 0.003 inches to obtain higher flow rates since such increases will lead to lower homogenization efficiencies.
• the valve seat is a knife-edge configuration.
• the valve seat 158 is chamfered at 45° angle sloping toward the valve surface 156.
• the valve seat 158 is flat across a distance of ideally approximately 0.015 to 0.020 inches, but less than 0.06 inches.
• the valve seat slopes away from the valve surface at an angle from 5 to 90° or greater, 45° in the illustrated embodiment .
• valve gap region 160 fluid passing through the valve gap 102 is accelerated as it passes over the relatively short valve seat or land 158.
• the adjoining valve member presents a flat valve surface 156 that extends radially outward, parallel to the direction of fluid flow through the gap 102.
• the total length of the valve surface extending radially from the land is not a closely controlled tolerance but tends to be relatively long, approximately 0.055 inches in length.
• Fig. 4 illustrates the flow conditions for fluid passing through the prior art valve gap region 160.
• flow between the land 158 and the valve surface 156 is entirely laminar 180. Little homogenization occurs in this space, but the fluid is highly accelerated at this point.
• the portion of the fluid 180 in laminar flow reduces with increasing distance from the gap 102.
• the layers away from the valve surface 156 are progressively converted into turbulent three dimensional high and low speed mixing layers 182 in which the laminar characteristics do not exist.
• the energy dissipation in the turbulent mixing layer peaks and a homogenization front or zone 184 forms in which the mixing layers merge and become fully turbulent . This is where most of the homogenization occurs. It is here that the energy contained in the fluid's pressure and speed is converted into the disruption of the milk fat globules or the blending of components in the emulsions or dispersions, generally.
• the location of the homogenization front can be defined two ways. For a common valve gap for milk homogenization of 0.0018 inches, the homogenization front is centered at approximately 0.012 inches from the end 187 of the land surface. More generally, however, the homogenization front stretches across a distance of approximately 6 to 10 times the size of the gap. This relationship can be generalized to other valve configurations .
• valve gap region 170 in the valve gap region 170 according to the present invention, the ends of the opposed surfaces that define the gap 102 are still staggered with respect to each other.
• the valve surface 156 terminates 188 much closer to the end of the land 158. There is some overlap, but the length of the overlap is closely controlled.
• Fig. 5 shows the flow conditions for the fluid emerging from valve gap 102 when no overlap exists.
• the region of laminar flow 180 exhibits a triangular cross- section extending away from the valve gap, decreasing on its top and bottom moving away from the ends of the valve surfaces.
• the homogenization zone or front 184 converges with the turbulent mixing layers 182. Virtually all fluid that exits from the valve passes through this zone existing at approximately 5 gap distances and is completely homogenized.
• valve surface 156 and valve seat 158 wall effects from the valve surface 156 and valve seat 158 will not otherwise arise as long as the chamfering angle ⁇ , which is illustrated as 45 degrees, does not approach the angle of divergence of the turbulent mixing layer, ⁇ , which is 5.7 degrees.
• the angle ⁇ is at least 10 degrees to avoid the risk of any attachment of the laminar flow to the wall.
• Fig. 7 is a plot presenting the results of experiments correlating mean globule diameter in homogenized milk as a function of pressure for valves using different overlaps.
• Valve overlaps between 0.025 inches (D) , 0.040 inches ( ⁇ ) and the standard 0.055 inches (•) exhibit essentially the same performance.
• a mean globule size of approximately 0.90 micrometers is produced between 1,100-1,200 psi homogenizing pressure.
• overlaps of 0.010 (•) or 0.0 inches (no overlap) ("ft) are used, however, the mean globule diameter drops to approximately 0.80 micrometers in the same range of homogenizing pressures. This experimentation shows that overlaps less than 10 valve gaps long, or approximately 0.025 inches, obtain substantially better homogenization.
• Fig. 8 shows the results of experimentation using a laboratory setup with a corresponding low flow rate.
• the plot is of droplet diameter as a function of overlap or overhang for three homogenizing pressures (1000 psi (o) , 1200 psi (D) , and 1400 psi ( ⁇ ) ) using filled milk at a flow rate of 40 gallons per hour. Even at this low flow rate, a reduction in overlap yields better homogenization, agreeing with the experiments under commercial conditions.

Landscapes

• Chemical & Material Sciences (AREA)
• Dispersion Chemistry (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Dairy Products (AREA)
• Soy Sauces And Products Related Thereto (AREA)
• Lift Valve (AREA)

Priority Applications (2)

Applications Claiming Priority (3)

Publications (3)

Family

ID=25220153

Family Applications (1)

Country Status (11)

Families Citing this family (24)

Family Cites Families (28)

• 1997
  • 1997-03-13 US US08/816,278 patent/US5749650A/en not_active Expired - Lifetime
• 1998
  • 1998-03-11 CA CA002283930A patent/CA2283930C/en not_active Expired - Lifetime
  • 1998-03-11 DK DK98909117T patent/DK0966320T3/da active
  • 1998-03-11 ES ES98909117T patent/ES2226104T3/es not_active Expired - Lifetime
  • 1998-03-11 EP EP98909117A patent/EP0966320B2/de not_active Expired - Lifetime
  • 1998-03-11 AT AT98909117T patent/ATE273062T1/de not_active IP Right Cessation
  • 1998-03-11 CN CN98803288A patent/CN1120744C/zh not_active Expired - Lifetime
  • 1998-03-11 AU AU66981/98A patent/AU724832B2/en not_active Expired
  • 1998-03-11 JP JP53976798A patent/JP4163261B2/ja not_active Expired - Lifetime
  • 1998-03-11 DE DE69825569T patent/DE69825569T3/de not_active Expired - Lifetime
  • 1998-03-11 WO PCT/US1998/004775 patent/WO1998040156A1/en active IP Right Grant
  • 1998-05-11 US US09/076,297 patent/US5899564A/en not_active Expired - Lifetime

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events